Philippine marine macroalgae as sources of bioactive natural products and macronutrients for food applications

The coastal waters of the Philippine archipelago harbor a remarkable diversity of macroalgae (seaweeds), representing a valuable yet underexplored resource for food, medicine, and biotechnological applications. Several species are traditionally consumed as fresh salads in the Philippines, offering dietary benefits such as essential minerals, macronutrients, and antioxidants. At the same time, some macroalgae produce bioactive natural products that may serve as pharmaceutical leads, though in certain cases, these compounds could pose toxicological risks to consumers. In this study, we evaluated the proximate chemical composition of 27 macroalgal samples and assessed the cytotoxic potential of all 59 samples, comprising 31 red (Rhodophyta), 16 green (Chlorophyta), and seven brown (Heterokontophyta) taxa, collected from seven provinces across the Philippines. Extracts were analyzed for carbohydrate, phenolic, and protein content, as well as cytotoxic activity against cancer cell lines. On average, Rhodophyta species exhibited the highest carbohydrate content, while Chlorophyta samples showed slightly elevated levels of protein and polyphenols. Cell-based toxicity assays were used both to screen for potential drug leads and to detect possible toxic constituents. In several cases, specifically two Heterokontophyta, two Rhodophyta, and one Chlorophyta, natural products were isolated and structurally elucidated using mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and other analytical techniques. Notably, in at least one case, epiphytic cyanobacteria were the source of toxins associated with the extract of a field collected rhodophyte, Gelidiella acerosa.